A major health project that Apple has been working on since at least 2020 is a blood pressure cuff system that may work with an iPhone or Apple Watch: 01, 02, 03, 04, 05 and 06. Today, the U.S. Patent and Trademark Office officially granted Apple a patent for another take on a blood pressure cuff system.

Blood Pressure Measurement Using Device With Single and Multiple Piezoelectric Sensors

Apple's granted patent relates to devices for determining blood pressure measurements and other biological parameters. The blood pressure measurement devices may include one or more piezoelectric sensors (e.g., differential piezoelectric sensors) for detecting blood flow through limbs of users as part of determining blood pressure measurements. In some cases, the piezoelectric sensors may additionally or alternatively be used to determine one or more biological parameters of users (e.g., a ballistocardiogram, a heart rate, a heart rate variability, and a pulse wave velocity).

The blood pressure measurement devices described in this patent may include one or more capacitive sensors for detecting a pressure applied to the arm of the user by the blood pressure measurement devices and/or operational states of the blood pressure measurement devices (off-arm, on-arm, inflating, deflating, and the like).

The blood pressure measurement devices may include a cuff that extends around a limb (e.g., an arm or a leg) of a user. The cuff may include an inflatable bladder, and when the inflatable bladder is in an inflated state, the cuff may occlude one or more blood vessels (e.g., veins, arteries, etc.) of the user. The piezoelectric sensor and/or the capacitive sensor may be coupled to the inflatable bladder or elsewhere along the cuff.

The blood pressure measurement devices may include a processing unit that causes the inflatable bladder to inflate to the inflated state. The air pressure within the inflatable bladder in the inflated state, and therefore the pressure exerted on the arm by the cuff may vary for different users. In some cases, the air pressure in the inflated state may be determined based on an estimation of a systolic blood pressure of the user, and so it may differ based on different estimated systolic blood pressures. The processing unit may cause the inflatable bladder to deflate during a deflation sequence in which air is gradually released from the inflatable bladder to reduce the pressure exerted on the arm by the cuff.

The piezoelectric sensor may be used to detect blood flow through the limb of the user during the deflation sequence, and output signals corresponding to the blood flow. The signals output by the piezoelectric sensor may correspond to vibrations, sounds, or other disturbances resulting from changes in the blood flow through vessels in the limb as the pressure exerted on the arm by the cuff changes. In some cases, the signal output by a piezoelectric sensor during a deflation sequence includes an oscillometric waveform corresponding to arterial pressure changes within the artery of the user. In some cases, the signal output by a piezoelectric sensor during a deflation sequence includes sounds (e.g., Korotkoff sounds) corresponding to turbulent flow through a partially-occluded artery.

The capacitive sensor may output a pressure signal corresponding to the pressure applied to the arm of the user during the deflation process. The processing unit may correlate the oscillometric waveform and/or the sounds present in the signal output by the piezoelectric sensor to the pressure signal to determine estimated blood pressure measurements. The processing unit may determine an oscillometric blood pressure measurement, which may include determining an estimated mean arterial pressure corresponding to the value of the pressure applied to the arm during a peak oscillation of the oscillometric waveform. Additionally or alternatively, the processing unit may determine an auscultatory blood pressure measurement, which may include determining an estimated systolic blood pressure corresponding to the value of the pressure applied to the arm when a first Korotkoff sound is detected, and/or an estimated diastolic blood pressure corresponding to the value of the blood pressure applied to the arm when a final Korotkoff sound is detected.

In some cases, the signal output by the piezoelectric sensor may be used to determine estimated blood pressure measurements using both oscillometric and auscultatory methods. The processing unit may filter the signal output by the piezoelectric sensor to isolate the oscillometric waveform and/or the Korotkoff sounds as part of determining oscillometric and/or auscultatory blood pressure measurements.

In some cases, the blood pressure measurement device may be used to determine one or more biological parameters in addition to or instead of determining a blood pressure measurement. Biological parameters may include a ballistocardiogram, a heart rate, a heart rate variability, or a pulse wave velocity, and the like. In various embodiments, the signals output by the piezoelectric sensor may include biological waveforms corresponding to biological parameters. The processing unit may filter the signals output by the piezoelectric sensor to isolate the biological waveforms, which may then be used to determine the biological parameters. In some cases, the blood pressure measurement device may include one or more additional or alternative sensors for detecting signals for determining biological parameters.

Apple's patent FIG. 1 below illustrates an example blood pressure measurement device as worn by a user; FIG. 2 illustrates the example blood pressure measurement device of FIG. 1 in a closed configuration.

Apple's patent FIG. 3 below is a chart that illustrates how isolated waveforms may be correlated to a pressure signal to determine oscillometric and/or auscultatory blood pressure measurements. 

Apple's patent FIG. 7 above illustrates an example blood pressure monitoring device with multiple piezoelectric sensors.

For more details, review Apple's granted patent 11744476.